And if you live near Plenty Road in Bundoora and rely on the route 86 tram, you're in the worst spot in Melbourne.

The stop at the corner of Plenty Road and Greenwood Drive is the worst myki dead zone in Victoria for trams. If you forget your card or are out of credit, it's a 1.5 kilometre walk to the nearest post office to top up.

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If you do not have any credit on your myki you are expected to take reasonable steps to top up, but from these locations you rack up at least 1200 paces to get to the nearest store or machine.

Using the interactive below, you can detect myki dead zones on your tram line and find out where the nearest myki retailer is, in case you ever find yourself short on credit.

Just enter in your tram route and select your stop to bring up the distance, as the crow flies, to your nearest top-up point. Are you in the middle of a myki desert?

The colour scale changes depending on the tram route and should not be used to compare tram lines. (Scroll down for a map showing myki retailer distance for all tram routes).

But keep in mind the opening times of the retailer. When we trekked 1.5 kilometres through Melbourne's biggest myki desert on a scorching 31 degree day to top up at Bundoora Post Office, we were fortunate enough to get there half an hour before closing time.

But we would have been out of luck after 5pm that afternoon, after midday on Saturday, or when it is closed all day on Sunday.

About 95 per cent of the state's 800-plus myki retail outlets are open on Saturday, 75 per cent on Sunday and 32.5 per cent are open all hours. There are also myki-dispensing machines at railway stations and premium trams stops, which are available 24/7.

And while you can't top up on a tram, you can on a bus. So if you're at the Greenwood Drive tram stop, you could wait for the 382 bus then ask the driver to top up your card. But with buses at 40-minute intervals, you could be in for a lengthy wait.

Daniel Bowen of the Public Transport Users Association said the inability to top up on a tram has been a problem ever since myki was introduced.

"Myki was originally planned to include ticket machines on-board trams. It's never been explained why this was scrapped, and it would make sense for the government to revisit this decision," he said.

"While it's true that online options are available, it can take hours for an online top-up to take effect," he said. "This is particularly problematic for older Victorians, who may not have internet access."

Public Transport Victoria spokesman Jake McLaughlan said recent improvements to the myki system such as faster online top-ups and contactless payment options had made it easier for passengers.

He said the government had also introduced a simpler and fairer fare enforcement system that targets repeat fare evaders and provides more discretion to passengers who make every reasonable attempt to travel with a valid myki.

Is this discretion being used by ticket inspectors? If you live near a myki desert you'll probably be about to find out.

This map of the entire tram zone shows myki deserts in red. If you click a tram stop, a box will appear showing the distance to the nearest retailer and the distance to the nearest bus stop (where you can get the bus driver to top up your card). The scale on this map is fixed so it allows for comparisons between tram routes.